The present invention is generally related to systems for providing information for use in determining the ink requirements for a printing press. More particularly, the present invention is directed to an apparatus for analyzing an image member, such as a photographic film or lithographic plate which bears an image to be printed and provides output information representative of the image area.
In many printing processes, particularly offset printing, the thickness of ink film applied to a printing member, such as a lithographic plate, is controlled by regulating the quantity of ink in each of a plurality of adjacent columns on the service of the printing member. In many cases, the quantity of ink presented to each column is controlled by a deformable blade or other means which is spaced at an adjusted distance from an inking roll by means of adjustable keys or other regulating means for each column. In some cases, each column may be supplied with ink by a piston pump which is controlled to vary the amount of ink supplied to each column.
In the past, it has been common to adjust the amount of ink by observing the printed product to determine which columns are receiving too much or too little ink and adjusting the ink keys accordingly. An initial adjustment may be made by merely observing the overall image area with the naked eye and adjusting the ink keys to an approximate setting.
In U.S. Pat. No. 4,180,741 there is disclosed a system for obtaining information on the ink requirements in which a scanner assembly is moved across a photographic film on a transparent support surface. The assembly carries a light source and sensor head including a columnar array of light sensors. The photographic film (positive or negative) represents an image area divisible into a plurality of columns corresponding to adjacent ink key columns. Calibration strips are provided at either or both ends of the transparent support surface to calibrate the light sensors and compensate for variations in film type and thickness. The calibrated and processed data samples for each column to be printed provide image area information for the respective columns. These values may be stored or are utilized immediately as inputs to the printing press to make initial ink key settings.
Although the system disclosed in U.S. Pat. No. 4,180,741 provides several significant advantages over the prior systems for obtaining information for initial ink key settings, it is limited to the scanning of a positive or negative photographic film or the like containing transparent areas, the system could not be utilized for obtaining information from printing plates such as utilized in a lithographic process.